The present invention relates generally to fuel injectors for gasoline engines, and more particular to a unit injector for such engines.
A typical gasoline injector for an automotive engine is connected to a fuel rail which is pressurized to a relatively low pressure. Such pressure is typically in the vicinity of 268 kilo-pascals or 39 PSI. It has proved exceedingly difficult to generate a properly atomized fuel spray pattern at the injector metering orifice due to this low pressure fuel. Further, since known fuel injectors are often attached directly to the engine, the heat of the engine will cause air bubbles to form within various fuel chambers of the fuel injector. Such air bubbles will cause a cycle to cycle variation in the performance of the fuel injector. The formation of these air bubbles is enhanced by this low pressure. It is an object of the present invention to provide a gasoline fuel injector which is communicated to a relatively low source of pressurized fuel and which includes means for increasing such fuel pressure to at least approximately 6895 KPA. It is a further object of the present invention to provide a fuel injector characterized by a finely atomized fuel spray. Another object of the present invention is to provide a fuel injector in which the rate of formation of air bubbles is significantly reduced or eliminated.
Accordingly, the present invention comprises:
A unit injector adapted to receive fuel from a relatively low pressure source, comprising:
a housing, armature means responsive to an electromagnetic force for opening and closing a metering orifice to control the ejection of fuel therefrom and various fuel receiving chambers disposed about the armature means and upstream of the metering orifice.
The injector further includes a check valve disposed upstream of the fuel receiving chambers, responsive to a pressure differential thereacross to control the flow of f uel to such chambers and first accumulator means disposed in first of the fuel receiving chambers, compressable in response to the pressure of the fuel therein for pressurizing the fuel in the various fuel receiving chambers and for controlling the rate at which fuel is ejected.
An outer bellows, received about a portion of the housing, fluidly sealed at one end, and adapted to expand and contract as fuel is received and purged therefrom, including a flexible, springlike wall effective to restore the outer bellows to its non-expanded size.
The injector further includes means defining a pressure chamber, means for communicating fuel to and from the bellows to the pressure chamber, means movable with the outer bellows to pressurize the fuel in the pressure chamber and for urging same across the check valve, to pressurize the fuel in the various fuel receiving chambers, compressing the first accumulator means (180), and means for generating the electromagnetic force to move the armature means away from the metering orifice.
In one embodiment of the invention the movoable means includes a cylindrical shaped piston while in another embodiment of the invention such means includes a cup-shaped piston having an insulative liner.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.